Angels by Carl Ruggles is originally written for six trumpets, in 1921. This recording is from 1938. The artists  in the Brass Ensemble is unknown, but they were lead by Gerard Schwarz. In 1940, Ruggles rescored the work for trumpets and trombones.

Charles “Carl” Sprague Ruggles (March 11, 1876 – October 24, 1971) was an American composer of the American Five group. He wrote finely crafted pieces using “dissonant counterpoint”, a term coined by Charles Seeger to describe Ruggles’ music. His method of atonal counterpoint was based on a non-serial technique of avoiding repeating a pitch class until a generally fixed number such as eight pitch classes intervened. He wrote painstakingly slowly so his output is quite small. [source]

Photo: Carl Ruggles at work table by John Atherton, ca. 1950.

The complete work of Ruggles (including Angels) can be found on the double album “Carl Ruggles – The Complete Music Of Carl Ruggles”, released in 1980 on Avant Garde Project.